1. Field of the Invention:
The present invention is directed to the field of vacuum sputtering deposition and more specifically to improvements in the area of cylindrical post magnetron systems.
2. Description of the Prior Art:
It is well known that when an electrical discharge is created between two electrodes at low gas pressure, the cathode electrode (often referred to as the target) is eroded due to the bombardment of ionized gas molecules thereon. The bombardment of gas molecules onto the cathode material strips atoms therefrom and those atoms are transported to condense on surrounding surfaces. The target cathode can be of any material or combination of materials including metals, alloys and semiconductors. Due to the high energy levels involved, the liberated atoms of cathode material are caused to travel in the ionized gas and arrive at a surface at such speeds as to give some degree of adhesion.
More intense bombardment rates of gas molecules at the cathode have been achieved through the use of specially designed magnetic fields that confine the electrons and consequently the ionized gas in closed loop paths at the surface of the cathode.
Magnetic confinement of electrons has also been instrumental in reducing the amount of substrate heating caused by the impingement of the energetic electrons onto the substrate surfaces.
U.S. Pat. Nos. 3,884,793; 3,995,187; 4,030,996; 4,031,424; 4,041,353; and 4,126,530 are commonly directed to cylindrical post magnetron systems which utilize an externally generated magnetic field having defined field flux lines that run parallel to the length dimension and surface of the cylindrical target-cathode. The systems described in the aforementioned patents produce efficient sputtering of the cathode-target material from a cylindrical post magnetron over a 360.degree. range. However, the systems are cumbersome, in that the external solenoid coils used to generate the external magnetic fields are relatively massive with respect to the cathode-target cylinder. Furthermore, due to the parallel magnetic field requirement, the system vacuum enclosure must be either constructed of a non-magnetic material or it must be sufficiently large enough to enclose the field generating coils and place the coils detrimentally within the vacuum chamber.
U.S. Pat. Nos. 4,179,351 and 4,221,652 are directed to cylindrical magnetron sputtering sources, each utilizing a tubular cylindrical target-cathode and at least one cylindrical magnet coaxially mounted within the tubular cathode. Each internally mounted cylindrical magnet is oriented symmetrically about the axis of the target-cathode cylinder so as to generate a toroidal magnetic field tunnel defined by flux lines that lie in planes parallel to the axis of the target-cathode cylinder. The '351 patent describes its technique as an improvement over an external magnet generated field type of magnetron, in that it provides a sputtering apparatus suitable for the efficient deposition of material upon the interior surface of a substantially cylindrical workpiece. It further describes an advantage wherein the electrons and charged ions are effectively confined to a volume proximate to the cathode surface, by the use of small permanent magnets.
It is noted that the toroidal fields generated in the devices described in the '351 and '652 patents may cause uneven and inefficient removal of the cathode surface material forming circular grooves in the cathode, that may be overcome by producing relative oscillatory movement between the cathode surface and the magnetic field along the axis of the cathode.